Electrical resistor and method of making same



' April 16, 1946. J. M. zANDER 2,398,585

ELECTRICAL RESISTOR AND METHOD 0F MAKING SME Filed Aug. 1, 1944 INVNToR.

Jasoh VLZdm/cf- .BY/ I ATToRNEY Patented Apnl, 1946 UNITED STATES PATENT OFFICE ELECTRICAL RESIS'IOR AND METHOD 0F MAKING SAME Jason M. Zander, Chicago, Ill., assigner to Chicago vitreous Enamel Product Company,

Cicero, Ill., a corporation of Illinois Application August l, 1944, Serial No. 547,529

A(Cl. 20L-64) 2 Claims.

I'his invention to electrical resistors. More particularly it relates tov electrical resistors comprising a cylindrical, generally tubular core, an electrical resistance wire spirally wound smooth uniform coating of vitreous enamel and which will resist vsuicides. changes in temperature without fracturing. Particular dimculty has been met by axial shifting oi the coils of the spirally wound resistance wire during the iiring of the enamel coating thereon, The wire coils separate in bunches along the core as a result oi high sur-Y face tension of the fused enamel, A

As the enamel fuses during the firing thereof, the enamel coatingscmetimes splits and the surface tension on the fused semi-liquid enamel causes the coating to draw away from the split, thereby resulting in the widening of the split and often leaving a considerable gap in the coating. The wire coils are pulled away from each other at the said gap, thereby being drawn into bunches along the core. This phenomenon is often referred to in the arts as wire bunching. For obvious reasons this is objectionable.

It is an object of this invention to provide an improved method for the production of enamel coated wire-wound resistors which will not be subject to wire bunching" during the firing of the enamel.

It is another object oi this invention to produce a wire-wound electrical resistor having a fused coating of an enamel, the wire coils of the resistor being in the position as originally wound, and the enamel coating being smooth and uniform over the entire surface thereof.

Other objects of the invention will appear hereinafter.

The above objects may be accomplished, in general, by first applying to a wire-wound elecceramic material, for example, steatite porcelain, magnesium silicate or magnesium aluminum silicate.

The resistor core is wound in a conventional manner with an electrical resistance wire, for example, a nickel-chromium alloy or nickel-copper alloy wire, and the wire securely held in place Alli sistor units which will have a substantially trical resistor core, a clay slip (aqueous suspension of clay) and drying the same beforeA application, and firing, of enamel .on the outer surface thereof.

The resistor core is generally composed of a 55 manner.

by means of metal fastening tabs or connecting elements to which the ends ofthe wire are fastened to form an electricity conducting unit from one tab through the wire to' the other tab. The above described wire-Wound core is then provided .with a coating of a slip composed of slay, The

clay may be kaolin, ball clay, china .cl'ay or the like. Preferably, the slip, i. e., the aqueous suspension, is made somewhat 'thin and iiuid. As a general guide, the slip should be made sufilciently uid to flow between the wire coils to the core, and to drain from the spaces between the wire coils so as to leave a substantially uniform coating on the exposed surfaces or the core and the wire. The actual proportion of water to clayr in the slip will, of course, depend upon the gauge of the wire, the spacing of the wire coils, and the particular clay being used in the slip. It will be readily apparent that if the slip is too thick, it will not ilow betweenv wire coils but will bridge the space between coils and as a result a coating of uniform thickness on the wires and the core will .not be obtained. In general, the clay slip should contain between 3 and 30 parts water for l part solids and Preferably between 5 and. 10 parts water for 1 part solids.

The lay slip may be prepared in any suitable For example, the clay and the water may be mixed and ball-milled to obtain the desired dispersion of the clay in the water. The ball-milled product may then be diluted with water to the desired consistency.

The clay slip may be applied to the wire-wound core in any desired manner; for example, it may be applied by brushing, spraying or dipping. Preferably, the clay slip is applied to the wirewound core by dipping and then allowed to drain: forv example, by suspending by one end thereof. The clay slip is then dried on the wire-wound core. 'I'he drying is preferably accomplished by contact with the atmosphere at room temperature:however, forced air drafts, or even mild baking can be employed, if desired. to dry the I'he wire-wound core containing the dry coatinsr of .clay is then coated with a vitreous enamel slip in a known manner. Any vitriilable enamel may be used for coating the resistor unit without material damage oi splitting of the enamel, or "wire launching, during the firing of the enamel. Theenarnel slip is then dried and red in a known manner.

The present invention is illustrated by the accompanying drawing showing two stages in the manufacture of electrical resistors in accordance with my invention.

l is an enlarged fragmentary sectional View of a wire-wound core containing a clay bentonite nndercoating and a vitreous enamel slip overcoating.

Fig. 2 is e. similar fragmentary sectional view of the finished electrical resistor after ming of the structure shown in Fig. l.

Referring to Fig. i of the drawing, reference numeral. ii designates a tubular ceramic eore, upon which is siriirallyu wound a resistor wire 3. The end of the wire il shown in this drawing is welded, braned, or otherwise fastened at Iii te metallic tali W and is clamped iirmly about the core G. A clap slip o the type described above and designated by numeral i2 is shown in a sul)n stantially uniform layer about the core 8, the tab I and the wire 8. Although, in the stage of production shown in this drawing, the clay is dry and contains an 'overcoating I4 oi enamel slip, it will be readily apparent that the clay, when applied as a slip, was sumciently thin and ifiuid to flow in between wire coils and to drain from the spaces between coils to leave a more or less uniform coating.

In Fig. 2-of the drawing, in which like reference characters designate like parts, the enamel M has been fired. I t will he noted that the clay has now substantially vanished. Since the clay it present in a thin uniform layer, as shown in Fig. 1, the fusing of tneenamel during the tiring operation, permitted an absorption of the clay and thereby causing a firm adherence ot the enamel to the core i and the wire I.

Throughout the specification, reference to parts, percentages and proportions refers to parts. percentages and proportions by weight. unless otherwise speciiled.

Since it is obvious that :many changes and modiilcations can be made iii; the above described details without departing :irons the nature and spirit of the invention, it is to be understood that the invention is not to be limited by said details except as set forth in the appended claims.

I claim:

l. The method of making wire-wound elec trical resistors which comprises applying to a core wound 'with reeistance wire a coating o! a. elip comprising on aqueous Suspension oi a clay, the slip being suiiicientlyfiuid to ow between the wire windings and to drain from the spaces between windings to leave a substantially uniform coating on the surfaces contacted, drying said coating, applying a coating of a vitreous enamel slip over said dry clay coating, drying said enamel slip, and firing said enamel.

2. The method of making wire-wound electrical resistors which comprises applying to a core wound with resistance wire a coating of a slip comprising an aqueous suspension of a clay', the slip containing 3 to 30 parts by weight of water for each part solids, drying said coating, applying a coating of a vitreous enamel slip over said clay coating, drying said enamel slip and $5 firing said enamel.

JASON M. ZANDER. 

